0399. Evaluate Division
https://leetcode.com/problems/evaluate-division
Description
You are given an array of variable pairs equations
and an array of real numbers values
, where equations[i] = [Ai, Bi]
and values[i]
represent the equation Ai / Bi = values[i]
. Each Ai
or Bi
is a string that represents a single variable.
You are also given some queries
, where queries[j] = [Cj, Dj]
represents the jth
query where you must find the answer for Cj / Dj = ?
.
Return the answers to all queries. If a single answer cannot be determined, return -1.0
.
Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction.
Example 1:
**Input:** equations = [["a","b"],["b","c"]], values = [2.0,3.0], queries = [["a","c"],["b","a"],["a","e"],["a","a"],["x","x"]]
**Output:** [6.00000,0.50000,-1.00000,1.00000,-1.00000]
**Explanation:**
Given: *a / b = 2.0*, *b / c = 3.0*
queries are: *a / c = ?*, *b / a = ?*, *a / e = ?*, *a / a = ?*, *x / x = ?*
return: [6.0, 0.5, -1.0, 1.0, -1.0 ]
Example 2:
**Input:** equations = [["a","b"],["b","c"],["bc","cd"]], values = [1.5,2.5,5.0], queries = [["a","c"],["c","b"],["bc","cd"],["cd","bc"]]
**Output:** [3.75000,0.40000,5.00000,0.20000]
Example 3:
**Input:** equations = [["a","b"]], values = [0.5], queries = [["a","b"],["b","a"],["a","c"],["x","y"]]
**Output:** [0.50000,2.00000,-1.00000,-1.00000]
Constraints:
1 <= equations.length <= 20
equations[i].length == 2
1 <= Ai.length, Bi.length <= 5
values.length == equations.length
0.0 < values[i] <= 20.0
1 <= queries.length <= 20
queries[i].length == 2
1 <= Cj.length, Dj.length <= 5
Ai, Bi, Cj, Dj
consist of lower case English letters and digits.
ac
class Solution {
Map<String, Double> value;
Map<String, Set<String>> graph;
Set<String> visiting;
public double[] calcEquation(String[][] equations, double[] values, String[][] queries) {
// edge cases
// illegal arguments
value = new HashMap<>();
// build graph
graph = new HashMap<>();
for (int i = 0; i < equations.length; i++) {
String[] e = equations[i];
if (!graph.containsKey(e[0])) graph.put(e[0], new HashSet<String>());
if (!graph.containsKey(e[1])) graph.put(e[1], new HashSet<String>());
graph.get(e[0]).add(e[1]);
graph.get(e[1]).add(e[0]);
// store value
value.put(e[0]+e[1], values[i]);
value.put(e[1]+e[0], 1.0 / values[i]);
}
// dfs find path, get result
visiting = new HashSet<String>();
double[] res = new double[queries.length];
for (int i = 0; i < queries.length; i++) {
String[] q = queries[i];
double tmp = dfs(q[0], q[1]);
res[i] = tmp;
}
return res;
}
private double dfs(String from, String to) {
// exit
if (!graph.containsKey(from)) return -1.0;
if (from.equals(to)) return 1.0;
visiting.add(from);
double res = -1.0;
// look around
for (String next : graph.get(from)) {
if (visiting.contains(next)) continue;
// if (next.equals(to)) {
// res = value.get(from+next);
// break;
// } else {
double tmp = dfs(next, to);
if (tmp != -1.0) {
res = value.get(from+next) * tmp;
}
// }
}
visiting.remove(from);
return res;
}
}
/*
map store value
dfs find path
*/
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